As described in Japanese Laid-Open Patent Publication No. Sho 63-171173(1988), an electrostatic two-dimensional actuator has a metallic portion of a moving element which is separated from a stationary electrode by a predetermined distance in a predetermined direction. This will be explained with reference to FIGS. 1a to 3b. FIGS. 1a and 1b show a conventional movable element and FIGS. 2a and 2b show a conventional stationary element. In these drawings, 1a and 2a are sectional views and 1b and 2b are plan views. In the movable element 1 of FIGS. 1a and 1b, metallic plates 3a, 3b, 3c and 3d are buried at four positions into a plate 2 of an insulating material and a high dielectric thin film 4 is formed on the surface by sputtering, or the like. Four electrodes 7a, 7b, 7c and 7d shown in FIGS. 2a and 2b having the same area as the metallic plate 3 are formed by bonding or the like on the surface of the insulating material 6 of the stationary element so that when the stationary element is superposed with the movable element of FIGS. 1a and 1b, the electrodes are spaced apart in a predetermined direction and by a predetermined distance from the metal.
FIG. 3a is a sectional side view of the actuator constituted by superposing the movable element and stationary element shown in FIGS. 1a and 1b and 2a and 2b and FIG. 3b is a sectional view from its top. Here, when a voltage is applied to the electrode 7a of the stationary element, the metal 3a is attracted by the charge of the electrode 7a and the movable element 1 moves to the right in the drawing until the electrode 7a and the metal 3a completely overlap one another. When the voltage application is switched to the electrode 7b, the movable element likewise moves leftwardly downward in the drawing until the metal 3b overlaps the electrode 7b. In this manner, the conventional example variously changes the moving direction of the movable element by selecting a suitable sequence of voltage application to a plurality of electrodes and its magnitude to execute rough movements and fine movements.
The prior art described above involves the following problems. The first problem is that it does not particularly consider the metallic gap between the electrode dimension of the stationary element and the dimension of the metallic portion of the movable element between the electrodes, for if the metallic portion of the movable element deviates from the electrode of the opposed stationary element, it does not operate. Second, since the centroid of the movable element and the generation portion of the propelling force are not in conformity with each other, there can occur a case where a rotational force acts on the movable element. Also, in such a case, if the position relation between the movable element and the stationary element deviates to a great extent, the drop of the propelling force cannot be started. Third, the movement in one direction is made by the combination of one electrode of the stationary element and one metallic portion of the movable element. Accordingly, the movement can be made only inside the areas of the electrode and the metallic portion but cannot be made in a long distance.